>>> k1 = Key('SomeKind', 1)
<Key[{'kind': 'SomeKind', 'id': 1}]>
>>> k1.is_partial()
False
>>> k2 = Key('ParentKind', 1, 'ChildKind')
<Key[{'kind': 'ParentKind', 'id': 1}, {'kind': 'ChildKind'}]>
>>> k2.is_partial()
True
>>> k3 = Key('ParentKind', 2, namespace='foo')
>>> k3
<Key[{'kind': 'ParentKind', 'id': 2}, namespace='foo']>